The present invention relates in general to a device and a method to ream a hole to an accurate final diameter and cold work the hole to induce a beneficial residual stress that will enhance the life of the component by retarding the onset and growth of fatigue cracks in the hole.
When a hole is drilled or bored through a metal and enlarged by a reamer, cold work is often applied to the hole to enhance its fatigue life. FIGS. 1A to 1D illustrate the steps required for a conventional cold work after a hole is initially drilled. As shown in FIG. 1A, after a hole 12 is drilled through a material 10, a tapered mandrel 14 pre-fitted with a lubricated split sleeve 16 is used to insert through the hole 12 in the material such as aluminum, steel, titanium or other metals. The function of the disposable split sleeve 16 is to reduce mandrel pull force, to ensure correct radial expansion of the hole, to preclude damage of the hole, and to allow one-sided processing. In FIG. 1B, the mandrel 14 pre-fitted with the sleeve 16 is then drawn through the hole 12. In FIG. 1C, the mandrel 14 is withdrawn from the hole 12, and in FIG. 1D, the sleeve 16 is removed and discarded from the hole 12, which is then reamed to the final size as shown.
The process as shown in FIG. 1A to FIG. 1D is time consuming and requires a skilled technician to accomplish. In the case that a large number of holes on a structure such as an aircraft, this method is only employed where it is absolutely necessary. It is therefore a substantial need to develop a cold working and reaming process and device that does not only reduce labor and time consumption, but also reduce the overall cost for treating a large number of holes.